Method for manufacturing microelectromechanical system structure

ABSTRACT

Methods for manufacturing MEMS structures are provided. The method includes forming a first trench and a second trench in a MEMS substrate by performing a main etching process and etching the MEMS substrate through the first trench and the second trench to form a first through hole and an extended second trench by performing a first step of an over-etching process. The method further includes etching the MEMS substrate through the extended second trench to form a second through hole by performing a second step of the over-etching process. In addition, a width of the first trench is greater than a width of the second trench, and a height of the first trench is greater than ¾ of a height of the MEMS substrate, and a height of the second trench is smaller than ⅔ of the MEMS substrate.

PRIORITY CLAIM AND CROSS-REFERENCE

This Application claims the benefit of U.S. Provisional Application No.62/563,878, filed on Sep. 27, 2017, and entitled “Method formanufacturing microelectromechanical system structure”, the entirety ofwhich is incorporated by reference herein.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications,such as personal computers, cell phones, digital cameras, and otherelectronic equipment. Semiconductor devices are typically fabricated bysequentially depositing insulating or dielectric layers, conductivelayers, and semiconductive layers of material over a semiconductorsubstrate, and patterning the various material layers using lithographyto form circuit components and elements thereon.

Semiconductor devices may include micro-electro-mechanical systems(MEMS) structures, including inertial sensors applications, such asmotion sensors, accelerometers, and gyroscopes. Therefore, thetechnology of forming micro-structures with dimensions in the micrometerscale may be required.

Although existing manufacturing processes for MEMS structures may havebeen generally adequate for their intended purposes, as devicescaling-down continues, they may have not been entirely satisfactory inall respects.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It shouldbe noted that, in accordance with standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A to 1F illustrate cross-sectional representations of variousstages of forming a semiconductor structure, such as a MEMS structure,in accordance with some embodiments.

FIGS. 2A to 2E illustrate cross-sectional representations of variousstages of forming a semiconductor structure, such as a MEMS structure,in accordance with some embodiments.

FIG. 3 illustrates a cross-sectional representation of a semiconductorstructure, such as a MEMS structure, in accordance with someembodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the subject matterprovided. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Furthermore, spatially relative terms, such as “beneath,” “below,”“lower,” “above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly. It should be understoodthat additional operations can be provided before, during, and after themethod, and some of the operations described can be replaced oreliminated for other embodiments of the method.

Embodiments of methods for forming microelectromechanical system (MEMS)structures are provided. The methods may include etching a MEMSsubstrate to form a number of openings in the MEMS substrate. Theetching processes used for forming the openings may be adjustedaccording to the loading effect when forming openings with variouswidths, so that the yield of the resulting MEMS structure may beimproved.

FIGS. 1A to 1F illustrate cross-sectional representations of variousstages of forming a semiconductor structure, such as a MEMS structure100, in accordance with some embodiments. As shown in FIG. 1A, asemiconductor substrate 102 is received in accordance with someembodiments. In some embodiments, the semiconductor substrate 102 is acomplementary metal-oxide-semiconductor (CMOS) wafer at an intermediatestage of processing. In addition, the semiconductor substrate 102 has arecess 104 formed from the top surface of the semiconductor substrate102, as shown in FIG. 1A in accordance with some embodiments. The recess104 may be formed by, for example, etching, milling, a laser technique,combinations thereof, or the like.

The semiconductor substrate 102 may be a semiconductor wafer such as asilicon wafer. Alternatively or additionally, the semiconductorsubstrate 102 may include elementary semiconductor materials, compoundsemiconductor materials, and/or alloy semiconductor materials. Examplesof the elementary semiconductor materials may include, but are notlimited to, crystal silicon, polycrystalline silicon, amorphous silicon,germanium, and diamond. Examples of the compound semiconductor materialsmay include, but are not limited to, silicon carbide, gallium arsenic,gallium phosphide, indium phosphide, indium arsenide, and indiumantimonide. Examples of the alloy semiconductor materials may include,but are not limited to, SiGe, GaAsP, AlInAs, AlGaAs, GaInAs, GaInP, andGaInAsP.

In some embodiments, the semiconductor substrate 102 includes structuressuch as doped regions including wells and source/drain regions,isolation features including shallow trench isolation (STI), inter-leveldielectric (ILD) layers, and/or conductive features including gateelectrodes, metal lines, vias, and contacts.

A MEMS substrate 106 is disposed over the top surface of thesemiconductor substrate 102, as shown in FIG. 1B in accordance with someembodiments. In addition, the MEMS substrate 106 covers the recess 104of the semiconductor substrate 102 in accordance with some embodiments.In some embodiments, the MEMS substrate 106 is a silicon wafer.

The MEMS substrate 106 and the semiconductor substrate 102 may be bondedby direct bonding, fusion bonding, thermo-compression bonding, gluebonding, eutectic bonding, or the like. The bonding process may furtherinclude the application of heat or pressure. In some embodiments, theMEMS substrate 106 may be doped with p-type and/or n-type of dopants byperforming implantation processes or in-situ doping processes.

In some embodiments, the MEMS substrate 106 has a first region 108 and asecond region 110, which are designed to be removed, such as by beingetched, to form through holes in the MEMS substrate 106. The firstregion 108 has a first width W₁ and the second region 110 has a secondwidth W₂ that is greater than the first width W₁. In some embodiments,the first width W₁ is in a range from about 1.8 μm to about 2.5 μm, andthe second width W₂ is in a range from about 0.5 μm to about 1.5 μm. Insome embodiments, the difference between the first width and the secondwidth is in a range from about 0.5 μm to about 2 μm.

It should be noted that, although the first region 108 and the secondregion 110 are shown in FIG. 1B, the dotted lines in FIG. 1B are shownin order to provide a better understanding of the concept of theembodiments. That is, there may not be real interfaces at the edges ofthe first region 108 and the second region 110. In addition, the firstregion 108 and the second region 110 are made of the same material andhave the same height in accordance with some embodiments. In someembodiments, both the first region 108 and the second region 110 aremade of Si. In some embodiments, the first region 108 and the secondregion 110 have the same height H of the MEMS substrate 106.

As shown in FIG. 1B, the first region 108 may be divided into a topportion 112 having a height H₁ and a bottom portion 114 having a heightH₂ directly under the top portion 112. In addition, the second region110 may be divided into a top portion 116 having a height H₃, a middleportion 118 having a height H₄, and a bottom portion 120 having a heightH₅. It should be noted that the top portion 112 and the bottom portion114 of the first region 108 and the top portion 116, the middle portion118, and the bottom portion 120 of the second region 110 are shown inorder to provide a better understanding of the subsequent etchingprocess, but there may not be real interfaces, or material differences,between each portion.

Next, a main etching process 122 is performed to etch the first region108 and the second region 110 to form a first trench 124 and a secondtrench 126, as shown in FIG. 1C in accordance with some embodiments.More specifically, the top portion 112 of the first region 108 and a topportion 116 of the second region 110 are completely removed byperforming the main etching process 112. As described previously, thefirst width W₁ of the first region 108 is greater than the second widthW₂ of the second region 110. Therefore, during the main etching process112, the etching rate of the top portion 112 of the first region 108 isgreater than the etching rate of the top portion 116 of the secondregion 110 due to the loading effect. As shown in FIG. 1C, after themain etching process 122 is performed, the depth of the first trench 124is greater than the depth of the second trench 126.

In some embodiments, the etching gas used in the main etching process122 is SF₆. In some embodiments, SF₆ used in the main etching process122 has a flow rate in a range of about 267 sccm to about 296 sccm. Insome embodiments, SF₆ used in the main etching process 122 has a flowrate in a range of about 229 sccm to about 287 sccm. In someembodiments, a polymer gas, such as C₄F₈, is used in the main etchingprocess as a protection gas. In some embodiments, C₄F₈ used in the mainetching process 122 has a flow rate in a range of about 251 sccm toabout 279 sccm. In some embodiments, C₄F₈ used in the main etchingprocess 122 has a flow rate in a range of about 275 sccm to about 338sccm. In some embodiments, the main etching process 122 is performed forabout 105 sec to about 125 sec. In some embodiments, bias power used inthe main etching process 122 is in a range of about 50 W to about 128 W.In some embodiments, bias power used in the main etching process 122 isin a range of about 47 W to about 113 W.

As shown in FIG. 1C, the main etching process 122 is adjusted tocompletely remove the top portion 112 of the first region 108 and thetop portion 116 of the second region 110. Therefore, the height of thefirst trench 124 is substantially equal to the height H₁ of the topportion 112 of the first region 108, and the height of the second trench126 is substantially equal to the height H₃ of the top portion 116 ofthe second region 110. In some embodiments, the height H₁ is greaterthan ¾ of the height H of the first region 108. In some embodiments, theheight H₃ is smaller than ⅔ of the height H of the second region 110. Inparticular, the main etching process 122 may be designed to increase thedifference between the etching rates at the first region 108 and thesecond region 110 by enhancing the loading effect during the mainetching process 122, so that the resulting structure may have a betteryield and performance (Details will be described later).

After the main etching process 122 is performed, an over-etching processis performed to form a wider through hole at the first region 108 and anarrower through hole 110 at the second region 110 in accordance withsome embodiments. More specifically, during the over-etching process,the bottom portion 114 of the first region 108 is completely removedfirst due to its greater width W₁. After the bottom portion 114 iscompletely removed, the amount of etching gas in the second region 110increases, and therefore the etching rate at the second region 110 inthe over-etching process also increases, according to Le Chatelier'sprinciple. That is, although the parameters used in the over-etchingprocess are not changed during the whole etching process, the etchingrate of the second region 110 changes when the bottom portion 114 of thefirst region 108 is completely removed.

In some embodiments, SF₆ used in the over-etching process has a flowrate in a range of about 201 sccm to about 222 sccm. In someembodiments, SF₆ used in the over-etching process has a flow rate in arange of about 173 sccm to about 215 sccm. In some embodiments, C₄F₈used in the over-etching process has a flow rate in a range of about 251sccm to about 279 sccm. In some embodiments, C₄F₈ used in theover-etching process has a flow rate in a range of about 258 sccm toabout 319 sccm.

In some embodiments, bias power used in the over-etching process is in arange of about 5 W to about 48 W. In some embodiments, bias power usedin the over-etching process is in a range of about 5.6 W to about 54 W.In some embodiments, the over-etching process is performed for about 80sec to about 100 sec.

For a better understanding of the concept of the embodiments, a firststep 128 and a second step 130 of the over-etching process may bedefined accordingly. The first step 128 of the over-etching process isdefined as the etching process performed in the time period in whichboth the bottom portion 114 of the first region 108 and the middleportion 118 of the second region 108 are etched, as shown in FIG. 1C inaccordance with some embodiments. The second step 130 of theover-etching process is defined as the etching process performed in thetime period in which only the bottom portion 120 of the second region110 is etched, as shown in FIG. 1D in accordance with some embodiments.

More specifically, the first region 108 is completely removed by thefirst step 128 of the over-etching process to form a first through hole132 in accordance with some embodiments. In addition, the middle portion118 of the second region 110 is completely removed by the first step 128of the over-etching process to form the extended trench 126′. In someembodiments, the height of the extended trench 126′ is substantiallyequal to the sum of the height H₃ and H₄ and is greater than ¾ of theheight H of the second region 110. That is, the height H₅ of the bottomportion 120 of the second region 110 is less than ¼ of the height H ofthe second region 110 in accordance with some embodiments. The overetching process is adjusted to remove appropriate amount at both thefirst step 128 and the second step 130 so that the resulting structurecan have an improved performance. (Detail will be described later.)

After the bottom portion 114 of the first region 108 is completelyremoved, the over-etching process proceeds to the second step 130, asshown in FIG. 1E in accordance with some embodiments. During the secondstep 130 of the over-etching process, the bottom portion 120 iscompletely removed to form a second through hole 134 in the MEMSsubstrate 106.

In some embodiments, the etching rate of the bottom portion 120 of thesecond region 110 of the MEMS substrate 106 is greater than the etchingrate of the middle portion 118 of the second region 110. In someembodiments, the ratio of the etching rate of the bottom portion 120 tothe etching rate of the middle portion 118 is greater than about 1.1. Insome embodiments, the ratio of the etching rate of the bottom portion120 to the etching rate of the middle portion 118 is in a range fromabout 1.1 to about 1.8. In some embodiments, the etching rate of themiddle portion 118 is in a range from about 0.10 μm/cycle to about 0.14μm/cycle. In some embodiments, the etching rate of the bottom portion120 is in a range from about 0.14 μm/cycle to about 0.18 μm/cycle.

As described previously, when the bottom portion 114 is entirely removedby the first step 128 of the over-etching process, the etching rate ofthe second region 110 in the second step 130 of the over-etching processsuddenly increases. Therefore, it may require much less time thanexpected for the bottom portion 120 of the second region 110 to beentirely etched away. Accordingly, the main etching process 122 and theover-etching process, including both the first step 128 and the secondstep 130, are designed to control the amounts of the first region 108and the second region 110 removed in these etching process to preventtoo much over-etching at the second region 110.

After the second step 130 of the over-etching process is performed, anelement 136 may be formed between the first through hole 132 and thesecond through hole 134, as shown in FIG. 1E in accordance with someembodiments. In some embodiments, the element 136 is a movable elementlocated over the recess 104 of the semiconductor substrate 102 used in aMEMS device to allow for free movement in at least one axis. The element136 may be supported by hinges, springs, beams, or the like (not shown)which may extend from a static element. In some embodiments, both staticelements and movable elements are formed between the first through hole132 and the second through hole 134.

Afterwards, a cap substrate 138 is bonded to the MEMS substrate 106 toform a MEMS structure 100, as shown in FIG. 1F in accordance with someembodiments. In some embodiments, the cap substrate 138 is a cap waferincluding interconnect structures, such as through substrate via (TSV),inside (not shown). In some embodiments, the cap substrate 138 includesa recess 140 located over the element 136 of the MEMS substrate 106. Abonding layer (not shown) may be formed between the MEMS substrate 106and the cap substrate 138. For example, the bonding layer may include apolymer, an adhesive, a glass solder, a conductive material, or thelike.

As shown in FIG. 1F, the first through hole 132 and the second throughhole 134 are located between the recess 104 of the semiconductorsubstrate 102 and the recess 140 of the cap substrate 138 in accordancewith some embodiments. In addition, the sidewall of the first throughhole 132 and the sidewall of the second through hole 134 are not indirect contact with the semiconductor substrate 102 and the capsubstrate 138 in accordance with some embodiments.

Generally, an etch stop layer may be used in an etching process todecide when to stop the etching process. However, when a numbers ofopenings with various widths need to be formed in the same substrate,many factors, such as loading effect, need to be concerned when theetching processes are designed. As described previously, the mainetching process 122, the first step 128 of the over-etching process, andthe second step 130 of the over-etching process are designed inaccordance with the widths and the thicknesses of the first region 108and the second region 110, so that when the over-etching process speedsup during the second step 130, damage to the structures formed in thesubstrate 102 exposed by the second through hole 134 due to the loadingeffect may be prevented or decreased.

In particular, the main etching process 122 and the over-etching processincluding the first step 128 and the second step 130 are designed toslow down the etching rates at the second region 110 to prevent too muchover-etching below the second through hole 134. That is, it is designedto increase the difference between the etching rate at the first region108 and the etching rate at the second region 110 by enhancing theloading effect during the main etching process 122 and the first step128 and the second step 130 of the over-etching process. In addition,since the etching rate at the second step 130 of the over-etchingprocess may suddenly increase due to the first region 108 being entirelyremoved at the first step 128, the increase of the etching rate in thesecond stage 130 is also taken into consideration when these etchingprocesses are designed. Therefore, the amount of over-etching at thesecond through hole 134, the narrower through hole, may be decreased,and the accumulation of electrons under the second region 110 may alsobe reduced. It is found that the yield of the manufacturing processesdescribed above may be improved for more than 50% in some embodiments.In addition, the performance of the resulting MEMS structure 100 mayalso be improved.

FIGS. 2A to 2E illustrate cross-sectional representations of variousstages of forming a semiconductor structure, such as a MEMS structure200, in accordance with some embodiments. The processes for forming theMEMS structure 200 may be similar to the processes for forming the MEMSstructure 100 described above, except the etching processes used to formthrough holes are designed to prevent too much over-etching under thewider through hole. Some processes and materials used to form the MEMSstructure 200 may be similar to, or the same as, those used to form theMEMS structure 100 described previously and may not be repeated herein.

As shown in FIG. 2A, a MEMS substrate 206 is disposed over the topsurface of the semiconductor substrate 102 in accordance with someembodiments. In addition, the MEMS substrate 206 covers the recess 104of the semiconductor substrate 102 in accordance with some embodiments.The MEMS substrate 206 may be the same as, or similar to, the MEMSsubstrate 106 described previously and some details are not repeatedherein.

Similar to the MEMS substrate 106, the MEMS substrate 206 has a firstregion 208 and a second region 210 which are designed to be removed,such as etched, to form through holes in the MEMS substrate 206. Thefirst region 208 may have the width the same as the first width W₁ ofthe first region 108 and the second region 210 may have the width thesame as the second width W₂ of the first region 110 described above. Asshown in FIG. 2A, the first region 208 may be divided into a top portion212 having a height H₆ and a bottom portion 214 having a height H₇directly under the top portion 212. In addition, the second region 210may be divided into a top portion 216 having a height H₈, a middleportion 218 having a height H₉, and a bottom portion 220 having a heightH₁₀.

Next, a main etching process 222 is performed to etch the top portion222 of the first region 208 and the top portion 216 of the second region210 to form a first trench 224 and a second trench 226, as shown in FIG.2B in accordance with some embodiments.

In some embodiments, an etching gas used in the main etching process 222is SF₆. In some embodiments, SF₆ used in the main etching process 222has a flow rate of in a range of about 215 sccm to about 271 sccm. Insome embodiments, C₄F₈ used in the main etching process 222 has a flowrate of in a range of about 275 sccm to about 337 sccm. In someembodiments, a bias power used in the main etching process 222 is in arange of about 59 W to about 144 W.

In some embodiments, the height H₆ of the top portion 212 (i.e. theheight of the first trench 224) is greater than ¾ of the height H of thefirst region 208. In some embodiments, the height H₈ of the top portion216 (i.e. the height of the second trench 226) is greater than ¾ of theheight H of the second region 210. In particular, the main etchingprocess 222 may be designed to decrease the difference between theetching rates at the first region 208 and the second region 210 byminimizing the loading effect during the main etching process 222, sothat the resulting structure may have a better yield and performance(Details will be described later).

After the main etching process 222 is performed, an over-etchingprocess, including a first step 228 and a second step 230, is performedto etch through the first trench 224 and the second trench 226, as shownin FIGS. 2C and 2D in accordance with some embodiments. In someembodiments, the parameters used in the first step 228 and the secondstep 230 of the over-etching process are the same.

In some embodiments, a flow rate of SF₆ used in the over-etching processis in a range of about 207 sccm to about 254 sccm. In some embodiments,a flow rate of C₄F₈ used in the over-etching process is in a range ofabout 216 sccm to about 271 sccm. In some embodiments, a bias power usedin the over-etching process is in a range of about 4.4 W to about 43 W.

The first step 228 of the over-etching process is defined as the etchingprocess performed in the time period in which both the bottom portion214 of the first region 208 and the middle portion 218 of the secondregion 208 are etched, as shown in FIG. 2B in accordance with someembodiments. The second step 230 of the over-etching process is definedas the etching process performed in the time period in which only thebottom portion 220 of the second region 210 is etched, as shown in FIG.2C in accordance with some embodiments.

More specifically, the first region 208 is completely removed to form afirst through hole 232 and the middle portion 218 of the second region210 is completely removed to form the extended trench 126′ during thefirst step 228 of the over-etching process. In some embodiments, theheight of the extended trench 226′ is substantially equal to the sum ofthe height H₈ and H₉ and is greater than ⅘ of the height H of the secondregion 210. That is, the height H₁₀ of the bottom portion 220 of thesecond region 210 is less than ⅕ of the height H of the second region210 in accordance with some embodiments. The over etching process isadjusted to remove appropriate amount at both the first step 228 and thesecond step 230 so that the resulting structure can have an improvedperformance. (Detail will be described later.)

After the bottom portion 214 of the first region 108 is completelyremoved, the over-etching process proceeds to the second step 230 toform a second through hole 234 in the MEMS substrate 206, as shown inFIG. 2D in accordance with some embodiments.

In some embodiments, the etching rate of the middle portion 218 is in arange from about 0.14 μm/cycle to about 0.18 μm/cycle. In someembodiments, the etching rate of the bottom portion 120 is in a rangefrom about 0.18 μm/cycle to about 0.22 μm/cycle.

As described previously, the main etching process 222 and theover-etching process, including both the first step 228 and the secondstep 230, are designed to control the amounts of the first region 208and the second region 210 removed in these etching process to preventtoo much over-etching at the first region 210.

After the second step 230 of the over-etching process is performed, anelement 236 may be formed between the first through hole 232 and thesecond through hole 234, as shown in FIG. 2D in accordance with someembodiments. The element 236 may be similar to, or the same as, theelement 136 described previously and therefore the details of theelement 236 are not repeated herein. Afterwards, a cap substrate 238,similar to the cap substrate 138, is bonded to the MEMS substrate 206 toform a MEMS structure 200, as shown in FIG. 2E in accordance with someembodiments. In some embodiments, the cap substrate 238 includes arecess 240 over the element 236.

As described previously, the main etching process 222, the first step228 of the over-etching process, and the second step 230 of theover-etching process are designed in accordance with the widths and thethicknesses of the first region 208 and the second region 210. Inparticular, the main etching process 222, the first step 228 of theover-etching process, and the second step 230 of the over-etchingprocess may be designed to decrease the difference between the etchingrates at the first region 208 and the second region 210 by minimizingthe loading effect. Therefore, the amount of over-etching at the firstthrough hole 234, the wider through hole, may be decreased, and the riskof damaging the structure under the first region 208 may also bereduced. Accordingly, the performance of the resulting MEMS structure200 may be improved.

FIG. 3 illustrates a cross-sectional representation of a semiconductorstructure, such as a MEMS structure 300, in accordance with someembodiments. The processes for forming the MEMS structure 300 may besimilar to the processes for forming the MEMS structures 100 and 200described above, and therefore the processes and materials used to formthe MEMS structure 300 may be similar to, or the same as, those used toform the MEMS structures 100 and 200 described previously and may not berepeated herein.

Similar to the MEMS structures 100 and 200, the MEMS structure 300includes a MEMS substrate 306 located between the semiconductorsubstrate 102 and the cap substrate 138, as shown in FIG. 3 inaccordance with some embodiments. In addition, trenches 332, 334, and335 having different widths are formed in the MEMS substrate 306 inaccordance with some embodiments. Since the widths of the trenches 332,334, and 335 are different, the etching rate form forming these trenchesmay also be different during the same etching process due to the loadingeffect. Accordingly, a main etching process and an over-etching processmay be designed, as described previously and shown in FIGS. 1A to 2E, tohave appropriate etching rate at different stages of the etchingprocesses to prevent too much over-etching during the manufacturingprocesses for forming the trenches 332, 334, and 335.

The MEMS substrate 306 may include a first zone Z1, a second zone Z2,and a third zone Z3, and the trenches 332, 334, and 335 may be formed inthe different zones of the MEMS substrate 306 for different purpose. Insome embodiments, the trenches 332 are formed in the first zone Z1 todefine an element 342 between the trenches 332. The trenches 332 may besimilar to, or the same as, the first trenches 132 and 232 describedpreviously. In some embodiments, the element 342 is a movable elementformed in a sensing/moving combination zone.

In some embodiments, the trenches 334 are formed in the second zone Z2to define an element 344 between the trenches 334. The trenches 334 maybe similar to, or the same as, the second trenches 134 and 234 describedpreviously. In some embodiments, the element 344 is a ground elementformed in a grounding zone for transferring electrons to neutralize thestructure.

In some embodiments, the trenches 335 are formed in the third zone Z3 todefine an element 346 between the trenches 335. The width of thetrenches 335 may be greater than both the trenches 332 and 334. In someembodiments, the element 346 is formed in a periphery of the MEMSsubstrate 306. In some embodiments, the trenches 335 surround a numbersof movable elements, such as the elements 342 or 344 in the MEMSsubstrate 306 (not shown). In some embodiments, the width of the trench335 is in a range from about 100 μm to about 1000 μm. In someembodiments, the difference between the width of the trenches 332 or 334is in a range from about 100 μm to about 1000 μm.

It should be noted that, the arrangement of the trenches in FIGS. 1A to3 are shown for better understanding the concept of the disclosure, andthe scope of the disclosure is not intended to be limiting. That is, anumbers of trenches with various widths may be formed in a MEMSsubstrate and the pattern of these trenches may be designed according toits application.

As described previously, a main etching process (e.g. the main etchingprocesses 122 and 222), a first step of the over-etching process (e.g.the first step 128 and 228), and a second step of the over-etchingprocess (e.g. the second step 130 and 230) are designed in accordancewith the widths and the thicknesses of the desired through holes, sothat too much over-etching under these trenches may be prevented.

More specifically, the bias power and the flow rates of the etching gasused the main etching process and the over-etching process may beadjusted in accordance with the loading effect during these etchingprocesses. In some embodiments, the bias power and the flow rates of theetching gas used the main etching process and the over-etching processare adjusted to enhance the loading effect during these etching process,so that the amount of the over-etching under the narrower trench in theMEMS substrate can be decreased. In some embodiments, the bias power andthe flow rates of the etching gas used the main etching process and theover-etching process are adjusted to minimize the loading effect duringthese etching process, so that the amount of the over-etching under thewider trench in the MEMS substrate can be decreased. In addition, thedifference of the etching rates in the first step and the second step ofthe over-etching processes has also be considered when these etchingprocess are designed. Accordingly, the performance of the resulting MEMSstructure may be improved.

Embodiments of methods for manufacturing a MEMS structure are provided.The method may include forming a first through hole and a second throughhole in a MEMS substrate. A main etching process and an over-etchingprocess may be performed to form the first through hole and the secondthrough hole. In addition, the firth through hole and the second throughhole may have different widths and therefore the etching rates forforming the first through hole and the second through hole may also bedifferent due to the loading effect. Therefore, the main etching processand the over-etching process may be designed in accordance with thewidths of the first through hole and the second through hole to preventtoo much over-etching during the over-etching process. Accordingly, theyield for forming the MEMS structure and the performance of theresulting MEMS structure can be improved.

In some embodiments, a method for manufacturing a microelectromechanicalsystem (MEMS) structure is provided. The method for manufacturing amicroelectromechanical system (MEMS) structure includes forming a firsttrench and a second trench in a MEMS substrate by performing a mainetching process and etching the MEMS substrate through the first trenchand the second trench to form a first through hole and an extendedsecond trench by performing a first step of an over-etching process. Themethod for manufacturing a MEMS structure further includes etching theMEMS substrate through the extended second trench to form a secondthrough hole by performing a second step of the over-etching process. Inaddition, a width of the first trench is greater than a width of thesecond trench, and a height of the first trench is greater than ¾ of aheight of the MEMS substrate, and a height of the second trench issmaller than ⅔ of the MEMS substrate.

In some embodiments, a method for manufacturing a microelectromechanicalsystem (MEMS) structure is provided. The method for manufacturing amicroelectromechanical system (MEMS) structure includes disposing a MEMSsubstrate over a semiconductor substrate. In addition, the MEMSsubstrate includes a first region and a second region over a recess ofthe semiconductor substrate. The method for manufacturing a MEMSstructure further includes removing a top portion of the first regionand a top portion of the second region of the MEMS substrate byperforming a main etching process and removing a bottom portion of thefirst region and a middle portion of the second region by performing afirst step of an over-etching process, thereby etching through the firstregion of the MEMS substrate to form a first through hole. The methodfor manufacturing a MEMS structure further includes removing a bottomportion of the second region by performing a second step of theover-etching process, thereby etching through the second region of theMEMS substrate to form a second through hole. In addition, a width ofthe first region is greater than a width of the second region, and aratio of an etching rate of the bottom portion of the second region inthe second step of the over-etching process to an etching rate of themiddle portion of the second region in the first step of theover-etching process is in a range from about 1.4 to about 1.8.

In some embodiments, a method for manufacturing a microelectromechanicalsystem (MEMS) structure is provided. The method for manufacturing amicroelectromechanical system (MEMS) structure includes etching a topportion of a first region of a MEMS substrate to form a first trench anda top portion of a second region of the MEMS substrate to form a secondtrench and etching a bottom portion of the first region through thefirst trench to form a first through hole and a middle portion of thesecond region through the second trench to form an extended secondtrench by performing a first step of an over-etching process. The methodfor manufacturing a MEMS structure further includes etching a bottomportion of the second region through the extended second trench to forma second through hole by performing a second step of the over-etchingprocess. In addition, a difference between a first width of the firstregion and a second width of the second region is in a range from about0.5 μm to about 2 μm, and an ratio of an etching rate of the bottomportion of the second region to an etching rate of the middle portion ofthe second region is greater than about 1.1.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

1. A method for manufacturing a microelectromechanical system (MEMS)structure, comprising: forming a first trench and a second trench in aMEMS substrate by performing a main etching process; etching the MEMSsubstrate through the first trench and the second trench to form a firstthrough hole and an extended second trench by performing a first step ofan over-etching process; and etching the MEMS substrate through theextended second trench to form a second through hole by performing asecond step of the over-etching process, wherein a width of the firsttrench is greater than a width of the second trench, and a height of thefirst trench is greater than ¾ of a height of the MEMS substrate, and aheight of the second trench is smaller than ⅔ of the height of the MEMSsubstrate.
 2. The method for manufacturing a microelectromechanicalsystem structure as claimed in claim 1, wherein a difference between thewidth of the first trench and the width of the second trench is in arange from about 0.5 μm to about 2 μm.
 3. The method for manufacturing amicroelectromechanical system structure as claimed in claim 1, furthercomprising forming a movable element between the first through hole andthe second through hole.
 4. The method for manufacturing amicroelectromechanical system structure as claimed in claim 1, whereinthe width of the first trench is in a range from about 1.8 μm to about2.5 μm, and the width of the second trench is in a range from about 0.5μm to about 1.5 μm.
 5. The method for manufacturing amicroelectromechanical system structure as claimed in claim 4, whereinthe width of the second trench is in a range from about 0.5 μm to about1.5 μm.
 6. The method for manufacturing a microelectromechanical systemstructure as claimed in claim 1, wherein a ratio of an etching rate inthe second step of the over-etching process to an etching rate in thefirst step of the over-etching process is in a range from about 1.4 toabout 1.8.
 7. The method for manufacturing a microelectromechanicalsystem structure as claimed in claim 1, further comprising: disposingthe MEMS substrate over a semiconductor substrate; and disposing a capsubstrate over the MEM substrate, wherein the first through hole and thesecond through hole are located over a recess of the semiconductorsubstrate.
 8. A method for manufacturing a microelectromechanical system(MEMS) structure, comprising: disposing a MEMS substrate over asemiconductor substrate, wherein the MEMS substrate comprises a firstregion and a second region over a recess of the semiconductor substrate;removing a top portion of the first region and a top portion of thesecond region of the MEMS substrate by performing a main etchingprocess; removing a bottom portion of the first region and a middleportion of the second region by performing a first step of anover-etching process, thereby etching through the first region of theMEMS substrate to form a first through hole; and removing a bottomportion of the second region by performing a second step of theover-etching process, thereby etching through the second region of theMEMS substrate to form a second through hole, wherein a width of thefirst region is greater than a width of the second region, and a ratioof an etching rate of the bottom portion of the second region in thesecond step of the over-etching process to an etching rate of the middleportion of the second region in the first step of the over-etchingprocess is in a range from about 1.4 to about 1.8.
 9. The method formanufacturing a microelectromechanical system structure as claimed inclaim 8, wherein a difference between the width of the first region andthe width of the second region is in a range from about 0.5 μm to about2 μm.
 10. The method for manufacturing a microelectromechanical systemstructure as claimed in claim 8, wherein the top portion, the middleportion, and the bottom portion of the second region have the same widthand are made of the same material.
 11. The method for manufacturing amicroelectromechanical system structure as claimed in claim 8, wherein aheight of the top portion of the first region is greater than ¾ of aheight of the first region, and a height of the top portion of thesecond region is smaller than ⅔ of a height of the second region. 12.The method for manufacturing a microelectromechanical system structureas claimed in claim 11, wherein a height of the top portion of thesecond region is smaller than ⅔ of a height of the second region. 13.The method for manufacturing a microelectromechanical system structureas claimed in claim 8, wherein the first region and the second regionare made of the same material.
 14. The method for manufacturing amicroelectromechanical system structure as claimed in claim 8, furthercomprising forming a movable element in the MEMS substrate between thefirst through hole and the second through hole.
 15. The method formanufacturing a microelectromechanical system structure as claimed inclaim 14, wherein an etching gas used in the first step of theover-etching process is the same as an etching gas used in the secondstep of the over-etching process, and a flow rate of the etching gasused in the first step of the over-etching process is also the same as aflow rate of the etching gas used in the second step of the over-etchingprocess.
 16. The method for manufacturing a microelectromechanicalsystem structure as claimed in claim 8, further comprising: disposing acap substrate over the MEM substrate.
 17. A method for manufacturing amicroelectromechanical system (MEMS) structure, comprising: etching atop portion of a first region of a MEMS substrate to form a first trenchand a top portion of a second region of the MEMS substrate to form asecond trench; etching a bottom portion of the first region through thefirst trench to form a first through hole and a middle portion of thesecond region through the second trench to form an extended secondtrench by performing a first step of an over-etching process; etching abottom portion of the second region through the extended second trenchto form a second through hole by performing a second step of theover-etching process, wherein a first width of the first region isgreater than a width of the second region, a difference between thefirst width of the first region and the second width of the secondregion is in a range from about 0.5 μm to about 2 μm, and an ratio of anetching rate of the bottom portion of the second region to an etchingrate of the middle portion of the second region is greater than about1.1.
 18. The method for manufacturing a microelectromechanical systemstructure as claimed in claim 17, wherein a height of the first trenchis greater than ¾ of a height of the MEMS substrate, and a height of thesecond trench is smaller than ⅔ of the MEMS substrate.
 19. The methodfor manufacturing a microelectromechanical system structure as claimedin claim 17, further comprising forming a movable element between thefirst through hole and the second through hole.
 20. The method formanufacturing a microelectromechanical system structure as claimed inclaim 17, wherein the first width of the first region is in a range fromabout 1.8 μm to about 2.5 μm, and the second width of the second regionis in a range from about 0.5 μm to about 1.5 μm.